GROVELAND FOEMATION IN PELCH MOUNTAIN RANGE. 415 



in the lower formation, namely, that this time followed a period of great 

 stresses. Also a period of still later stress has afiPected the recrystallized con- 

 stituents of the schists, just as it has those of the quartzite and dolomite. It 

 is shown by lines of fracture crossing the slides along which ferric oxide has 

 infiltrated, and by occasional straining and bending of the quartz and mica. 

 Garnetiferous varieties of the schists are found in close proximity to 

 basic igneous rocks, probably in every instance intrusives, and are evidently 

 the result of contact metamorphism. With the garnets occur actinolite in 

 felted mats and clusters, and abundant magnetite and pyrite. A colorless 

 amphibole in large single crystals bounded by the prism and clinopinacoid, 

 and giving low extinctions, is often associated with the actinolite. 



SECTIOK VII. THE GROVELAISTD FORJUATIO^T. 



The ferruginous rocks which compose this formation are well exposed 

 in the central portion of sec. 31, T. 42 N., R. 29 W., in the vicinity of 

 the Groveland mine, and thus may properly be termed the Groveland 

 formation. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The magnetite, which is always an abundant constituent of these 

 rocks, has made it possible to trace them for long distances throughout the 

 trough, by means of the disturbances effected in the compass needles. The 

 same disturbances had led to the sinking of a great number of test pits on 

 the part of former explorers for iron ore, and the material thrown out of 

 these has served to check and substantiate the inferences from the magnetic 

 attractions. Finally, in several localities excellent natural exposures of the 

 iron-bearing- rocks occur. So, altogether, the available data as to the surface 

 distribution of the Groveland formation are fairly satisfactory. 



On the west the presence of the Groveland formation through sees. 34, 

 35, and 36, T. 42 N., R. 30 W., is shown by one principal and other minor 

 lines of attraction, as well as by test pits and outcrops. The principal line 

 of attraction begins in section 34, near the southwest corner, and runs to 

 the northeast, in conformity with the strike of the northern belt of dolomite, 

 finally ending in the northeastern portion of section 36. This line of attrac- 

 tion is very vigorous and strongly marked. Two other lines, parallel with 

 the principal line, but more feeble and much shorter, cross the boundary 

 between sections 35 and 36, and on the northern of these ferruginous rocks 



